Abstract

To contribute to the understanding of the sources, sinks, and radiative properties of black carbon (BC), the Department of Energy Atmospheric Science Program conducted a field experiment in 2006 in and around Mexico City. As a precursor to this experiment, measurements of BC and other aerosols were taken in Mexico City during 2003. In this study, analysis of these measurements were performed to understand the sources of the BC aerosols and to evaluate the significance of a primary sink. These issues were addressed using measurements of BC and related species from the following: measurements from the El Centro Nacional de Investigacion y Capacitacion Ambiental site, backward air-parcel trajectory calculations using HYSPLIT 4 model, and Fire Map derived from satellite datasets. Black carbon absorption measurements ranged from the IR band to the UV band. The dependence of the absorption on wavelength were hypothesized to be from (a) the BC during these periods were chemically different from the rest of the time series i.e. had a different source or (b) high values of relative humidity modified the locally emitted BC giving its absorption a dependence on wavelength. When comparing the backwards trajectories to the satellite pictures of the Yucatan Peninsula forest fires, the analysis showed that BC in the air was due to the forest fires during some of these times. The results of the correlation analysis between relative humidity and concentration of BC indicated only a few time periods with strong correlations. The correlation was not consistent enough to conclude that relative humidity was the only factor affecting the BC behavior. The analysis also showed that the rain events did not wash out all the BC in the air. Aerosol emission inventories in general do not include information resulting from burning of biomass or forest fires. Therefore, it is important to continue this study by analyzing the expanded data set provided by the DOE ASP 2006 field experiment. Studying the air quality in a megacity like Mexico City will help us understand more about the air pollution problems that exist throughout the world.